1. Field of Invention
This invention relates to intraocular optical lenses. More particular this invention relates to a prosthesis for replacing a part of the cornea of the eye, which has suffered for example severe corneal damage, and relates to a prosthesis for replacing the posterior lens of the eye which has variable power.
2. Prior Art & General Background
There are many cases of corneal blindness, caused by severe alkali burns, immunological disorders (e.g. Stevens-Johnson syndrome) cicatricial mucous membrane pemphigoid, or severe dry eyes where regular keratoplasty is not practical or has repeatedly failed. These corneas are often grossly opaque and densely vascularized with uneven thicknesses, associated with dense anterior and posterior synechiae, shallow or flat anterior chambers and cataracts or aphakia. In these situations only replacement of the cornea by a penetrating static keratoprosthesis effectively helps the patient. Current prosthetic designs require living tissue to bind to, through and around a hard polymethylmethacrylate (PMMA) prosthesis.
Keratoconus is a progressive disease of the cornea, which often results in an outward protrusion of the central area of the cornea, causing a thinning and disfigurement of the central cornea tissue. Since the cornea is basically a refracting surface for light rays received from the atmosphere, if the cornea is diseased with keratoconus, the resulting protrusion or cone distorts the normal refracting of the light rays, causing poor visual acuity and distortion. In addition, keratoconus is often very painful and irritable for the patient.
There are two known basic techniques which may be used to control or correct keratoconus. A first, more conventional technique, such as described in Siviglia, U.S. Pat. No. 4,601,556 issued on July 22, 1986, is to fit the patient with a special contact lens having a back or posterior surface, which is specifically designed to permit the diseased portion of the cornea to conform itself to the lens surface, resulting in both control of the keratoconus disease and improved visual acuity. Obviously, if the disease can be successfully controlled or corrected using such a special contact lens, a surgical corneal transplant can be avoided. However, for those cases in which the disease cannot be successfully controlled or corrected using a special contact lens, a surgical corneal transplant will be necessary.
Keratoplasty or corneal transplantation is a replacement of a partial (lamellar) or full (penetrating) thickness of diseased host cornea with donor tissue. Penetrating or lamellar keratoplasty may remove either a segment of, partial keratoplasty, or the entire, total keratoplasty, cornea. Improved techniques in cornea preservation, micro surgery and postoperative management have greatly increased the prognosis for penetrating keratoplasty during the past ten years. Previously "forbidden" corneal disorders are now being grafted successfully.
Although penetrating keratoplasty is quite successful, several factors can compromise the success of any graft. These include lid abnormalities, tear dysfunction states, recurrent forms of conjunctival inflammation, trigeminal dysfunction and neurotrophic keratitis, stromal vascularization, irregularities or extreme thinning of the stroma at the proposed graft-host junction, severe structural alteration to the anterior segment, active microbial or inflammatory keratitis, uncontrolled glaucoma and infancy.
When repeated grafts have failed, it is possible in an otherwise hopeless case to restore some vision by inserting a keratoprosthesis.
Initially the keratoprosthesis included a rigid, fenestrated, supporting plate with a removable threaded hard optical cylinder. The fenestrations or openings were to permit ingrowth of connective tissue and improve nutrition of the anterior corneal layers. Advances in this particular art led to a mushroom shaped transcorneal keratoprosthesis, such as that described in U.S. Pat. No. 4,470,159 to Peyman issued on Sept. 11, 1984. However, posterior fibrous coverings tend to extend over the optical portion, thus clouding of vision or even blindness may result, and inadequate anterior anchoring and ingrowth persists, and, although some prosthesis have remained successfully in place for years, others have been extruded in only weeks or months.
At the present time, the most commonly used prosthesis is an implant of a hard solid cylindrical polymethylmethacrylate lens in a flanged tubular element that protrudes posteriorly deep into the anterior chamber of the eye and which has biconvex anterior and posterior surfaces, forming a lens of appropriate power. The major complication with implants of this methylmethacrylate lens or "button" variety is that a firm bond between the cornea and the implant does not develop, and thus no barrier to infection from pathogens, which seems to occur subsequent to aqueous humor leakage from the anterior chamber around the optical center, is established, leading to extrusion with resulting endophtohalmitis and blindness. Secondary glaucoma may also be a severe complication with this type of prosthesis, because of the destruction of the outflow tracks. Thus the inability of corneal tissue to adequately infiltrate the edges of the implant to effect stabilization of the prosthesis and prevent aqueous humor leakage is a cause of many failures of these protheses.
Attempts have been made to provide a keratoprosthesis having a softer, more porous substrate surrounding the periphery of the cylindrical lens in the remaining lamellar cornea tissues. For the substrate, the patient's own tooth material, osterodentoceratoprostease, was used to provide the supporting structure.
Attempts have also been made to use a dacron peripheral skirt and supportive ungainal material, which have met with some postoperative success. Attempts have also been made to use a dacron velour skirted implant, but implants of this type have generally yielded unsatisfactory results. Perforations have also been replaced with radial slits, which gave for some of these embodiments better ingrowth results. However, good long term results were only obtained when implantation was accomplished by a slow surgical procedure requiring three operations, six to eight weeks apart. Although, these offered a slightly better visual field range, the prosthesis basically has a limited field of vision of less than fifty percent.
Attempts have also been made to employ a vitreous carbon alloplast, which is an inert carbon and "Teflon" mixture, as the material for anchoring corneal implants. The results, however, have been found less significant.
Cardona has also provided an implant having a flexible supporting plate, which improved the prosthesis ability to conform to corneal contours. The optical cylinder of the Cardona implant is threaded with an interpigmented cord to reduce glare. Extrusion of this type of prosthesis has been reduced in patients with thin corneas and pore conjunctiva, by having the central optical portion pass through the upper eyelid as well. The central optical element of this type of implant has been softened using a hydrogel disc in the cylindrical optic but with a rigid skirt, an example of this being the "hydrogel keratoprosthesis" of Binder (U.S. Pat. No. 4,586,929 issued May 6, 1986), having the same anchoring problems previously discussed.
It is also known that polyglyceryl methacrylate, a much softer and more hydrophilic polymer than polymethylmethacrylate, produced little or no implanatory changes in the cornea or interior chambers. However problems regarding suitable anchorings still persist.
Non-toxic silicone-rubber implants have also been encapsulated, and a ceramic keratoprosthesis having a ceramic form of alumina oxide with traces of magnesium oxide (A1.sub.2 O.sub.3 99.7% MgO 0.3%), which has a high refractive index and high wetability, has been relatively successful. However, anchoring the implant poses some difficult problems. Even with the use of sutures and cyanoacrylate glue, intermittent leakage of fluid around the cylinder has led to infection and extrusion.
Presently keratoprostheses are supported initially by sutures which are augmented by periosteum, fascia lata, Tenon's capsule and/or conjunctival flaps. Further, a significant amount of all keratoprosthetic operations requires some type of sutury operation, since complications due to uncontrollable glaucoma, optical overgrowth, conjunctival retraction, uveitis, retroprosthetic membranes and endophthalmitis are still prevalent, and the long-term visual acuity drops to little or no light perception in great than 50% of all the cases. Therefore, while the extrusion rates of keratoprosthetic devices have dramatically decreased, a successful implant material has not been found, which can mimic corneal properties enough to allow easy anchoring and adequate ingrowth in the eye. Without this, the prostheses will ultimately fail.
For a corneal implant which is entirely embedded in the cornea and which is not exposed to the atmosphere nor to the aqueous humus, see U.S. Pat. No. 4,607,617 to Choyce issued on Aug. 26, 1986. The corneal implant allows correction for defects in eyesight normally corrected by spectacles and contact lens and provides a surgical alternative to mitigate the defective eyesight.
Another type of disease, which may affect an intraocular element of the eye, is cataracts. A cataract is a progressive disease of the posterior lens behind the iris of the eye, causing clouding of the lens or of its surrounding transparent membrane that obstructs the passage of light. Since the posterior lens is basically a focussing element for focusing an image by focussing rays of light through the vitreous chamber and onto the retina in the back of the eye, which is varied by muscles within the eye, to focus on objects that are close or far away, the resulting clouding of the element causes eventual blindness.
It has been found possible to alleviate this condition by providing a static clear, hard disc having convex anterior and posterior surfaces, which is inserted into the eye and located in the capsular bag between the iris and the vitreous body, along with removal of the posterior lens (lensectomy) of the eye. As described in U.S. Pat. No. 4,615,701, these may be provided with haptics or flexible strands, which curve outward from the periphery of the lens that may be positioned close to the lens optic for ease of implantation and which are then released to move to the peripheral limits of the lens capsule, for centration and fixation of the intraocular lens for attaching the lens to the ciliary body which encircles the lens.
In some cases the disc is somewhat flexible and the ciliary body may provide some focussing control over the lens by means of the haptics. However, any control over this type of artificial lens is generally limited and any control over the focusing element may not provide adequate focusing of the lens to restore optimal vision to the patient. Further, with an artificial lens which is hard, additional refractive lens are necessary for good vision, as the hard disc is structurally adequate for optimum vision only at a single, set focal point.
Some attempts have been made to provide an intraocular prosthesis that provides accommodation in response to contraction and relaxation of the ciliary body. Accommodation is achieved by the motion of a lens or an element of a lens system, which have been implanted in a capsule, alternately toward and away from the fovea. Radially extending struts are provided which are biased radially inward, as the ciliary body contracts, forcing the lens toward the fovea, so that when the ciliary body is fully relaxed the lens is at its closest position to the fovea, and, as the ciliary body contracts, it counters the bias and causes the lens to move away from the fovea and toward the cornea.
For an example of a posterior lens of this type having a lens system implanted in a capsule, see U.S. Pat. No. 4,409,691 to C. F. Levy issued on Oct. 18, 1983. For another example of an intraocular lens that provides accommodation and response to contraction and relaxation of the ci1iary body, see for example U.S. Pat. No. 4,373,218 to R. A. Schachar issued on Feb. 15, 1983.
In the Schachar patent an intraocular lens having a fluid-expandable sack for containing a fluid. The fluid-expandable sack includes a lens portion and a valve portion which extends through the sclera of the eye. The fluid-expandable sack contains a fluid therein for providing the desired index of refraction, which may be either a gas or a liquid, and the index of refraction of the posterior chamber intraocular lens may be changed by adding or withdrawing fluid from the lens. However, no means is provided for attaching the lens element to the ciliary body and complications such as extrusion, retinal detachment and cystoid macula edema may still occur.
For additional patents relating to intraocular lens, see U.S. Pat. No. 4,615,701 to Woods issued Oct. 7, 1986, U.S. Pat. No. 4,615,702 to Koziol et al also issued Oct. 7, 1986, and U.S. Pat. No. 4,616,700 to Fedorov et al likewise issued Oct. 7, 1986.
Accordingly, it is an object of the method and apparatus of the present invention to provide an improved keratoprosthesis for the replacement of the diseased or injured, cornea, which method and apparatus differs from prostheses in current use, in that it does not protrude into the inner eye, but rather lies deep in an intralamellar stromal pocket and which is anchored in place by a fibrous ingrowth of tissue into a annular porous portion forming the periphery of the prosthesis. In accordance with this object, the method and apparatus of the present invention provides a lens or prosthesis having a convex anterior surface and a concave posterior surface, which has an annular porous ingrowth skirt extending radially from the periphery of the optic which, when optic positioned in an annular corneal incision extending annularly into the stroma of the cornea, allows fibrous ingrowth of the tissue into the skirt, thus anchoring the prosthesis in the sclera.
Further, the method and apparatus may provide spoke-like porous extensions, which are spaced around the periphery of the skirt and which extend radially therefrom and which are positioned in tunnels in the stroma of the cornea, which extend through the limbus into the sclera for allowing the forward progression of fluid from the anterior chamber to allow adequate nutrition and to avoid degeneration of the corneal connective tissue and corneal stroma of any remaining corneal tissue.
A further object of the keratoprosthesis is to provide a firm bond between the cornea and the prosthesis, so that no aqueous fluid can leak past the implant and therefore there is no direct entrance for pathogens into the eye. A further object of the keratoprosthesis is to provide a prosthesis having a similar disposition as the cornea of the eye, so that the patient may have a greater visual field and physicians may have a larger window for inspection of the inner eye. It is still a further object of the keratoprosthesis that noepithelial cells grow over its optic center and that the prosthesis-corneal shearing force has been eliminated, therefore eliminating extrusion. Another object of the keraprosthesis is that the patient have a better cosmetic appearance.
A further object of the method and apparatus is to provide a prosthesis lens which may be inserted into the eye and located in the capsular bag between the iris and the vitreous body for replacement of the posterior lens of the eye. Further, it is an object of the invention to provide a prosthesis for replacement of the posterior lens of the eye which is flexible and has means for attaching its lens element to the ciliary body, which surrounds the posterior lens of the eye, so that the lens element will change shape in response to ciliary body contraction in a similar manner as the normal posterior lens of the eye would.
3. General, Summary Discussion of the Invention
In accordance with these objects, the prosthesis of the present invention provide an elastomeric optical element having an annular skirt which surrounds the periphery of the element. Included with the skirt is an annular porous portion. The optical element is attached to the skirt by interpenetration of the periphery of the optical element into the pores of the porous portion.
The optical element may include convex anterior and posterior surfaces for replacement of the diseased or injured corneal button of the eye. An annular porous portion extending radially outwardly to periphery of the skirt is disposed in a lamellar incision which extends annularly into the stroma of the cornea surrounding the corneal button which is to be replaced.
A plurality of porous extensions, which may be six, extend radially outward from the periphery of the skirt and are located in tunnels extending radially through the limbus into the sclera. The extensions are entirely embedded and are not exposed to the atmosphere and allow forward progression of fluid by means of their pores from the anterior chamber of the eye to the sclera, thus allowing adequate nutrition of the sclera while avoiding degeneration of any remaining corneal stroma.
Tissue ingrowth into the pores of the porous portion connects and surrounds the prosthesis to the remaining corneal tissues, thus preventing aqueous fluid from leaking past the implant while allowing no direct path for pathogens into the eye.
The optical element may include biconvex anterior and posterior surfaces for replacement of the posterior lens of the eye between the iris and the vitreous body. A small incision is made, and the prosthesis is inserted through the incision and the opening in the iris and manipulated into the capsular bag. The natural lens of the eye can then be removed by any method such as lensectomy and cryoextraction.
The removal of the natural lens forms a void in the eye which is surrounded by the ciliary body, in which the prosthesis may be located, with its annular skirt in contrast with the zonular fibers and the ciliary body which surrounds the normal lens of the eye. Once the prosthesis has been manipulated into position, the incision may be sutured closed, allowing the prosthesis to stabilize and the zonular biers and the ciliary body to connect to the prosthesis through fibrous ingrowth into the pores of the porous portion of the skirt.